By Felicity Ogilvie for The World Today
ABC News Online, Fri May 8, 2009
http://www.abc.net.au/news/stories/2009/05/08/2565209.htm
A massive iceberg with enough freshwater in it to fill Sydney Harbour 135 times over is about to break off the Mertz glacier in Antarctica.
The iceberg will be 75 kilometres long and contains 750,000 gigalitres of ice which is apparently quite a lot.
Scientists are not sure if it is a natural event or if global warming is to blame. But a joint Australian and French team hope to find out.
The Mertz Glacier is near Commonwealth Bay in East Antarctica.
It flows into the southern ocean for 140 kilometres before it drops icebergs into the sea.
A large crack has formed about half way along the Mertz Glacier, which means it is going to drop a very large iceberg.
French glaciologist Benoit Legresy is measuring the break-up.
"Just at the moment, it's undergoing a massive calving event which promises to release an iceberg which will be between 20 to 25 kilometres wide and 75 kilometres long by about 400 to 500 metres thick," he said.
Melting ice
The iceberg contains enough fresh water to fill Sydney Harbour 135 times - that is 30 per cent of the world's annual water consumption.
When it breaks off, the iceberg won't melt straight away because it could take up to 30 years for the currents to move it to water that is warm enough to melt the ice.
The scientists realised the large iceberg was forming when they looked at satellite pictures of the Mertz Glacier and saw two large cracks. When the cracks kept getting bigger Benoit Legresy decided to measure the break-up.
"There's very few that have been picked up before the calving event, so we're in a pretty good situation where we are now, is we had the time to go on the glacier and put our instruments on it before the calving happens," he said.
Mr Legresy has put eight GPS beacons on the glacier to measure how the ice is moving.
"They are precise GPS beacons which are autonomous; they can operate as long as you're around and they measure the position where they are every 30 seconds, and this position is measured to almost a centimetre level," he said.
Two of the GPS beacons are on either side of a major crack on the Mertz Glacier.
PhD student Lydie Lescarmontier has been analysing the data from the beacons.
"We know that the speed of the opening is 12 centimetres per day for example and we can correlate this current for example and we know that when currents pushing the ice stone, we have an acceleration of the opening of the crack," he said.
The French scientists are spending this year working at the University of Tasmania with their Australian colleague, Professor Richard Coleman.
Natural phenomenon?
Professor Coleman is hopeful the research will give scientists a better idea of how glaciers work.
"We're trying to build up a picture of different cases, if you like different simulation studies to gain a better overall understanding of what's happening in the Antarctic region," he said.
"You're spending a year following, looking at how it's breaking up; will you be able to work out why? Whether this is a natural phenomenon or if it has anything to do with climate change?
"Realistically you need probably 50 or 60 years of data to see whether that's happening.
"What we're doing is building up a baseline study in effect so that we can see into the future and gain enough information from understanding the basic dynamics to then be able to model it.
"So one way that you can do it into the future is to build up numerical models and simulate whether if climate warms one degree or two degrees, how the ice shelf is going to react."
The scientists may be measuring the widening crack centimetre by centimetre - but they cannot say when the massive iceberg will finally break off the Mertz Glacier.
They are expecting it may break off before they get back down to Antarctica this summer.
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